The transmission is a very important part in speed change electric vehicles or electric hand tools. The whole speed change system typically represents about half of the production cost; therefore research on the speed change mechanism is always an important item for any company in the electric vehicle or the electric hand tool industry. A good transmission can change the rotational speed ratio according to different requirements. For use in an eclectic vehicle such as an electric bike, the transmission can be used to change the speed ratio so as to achieve the objective of an appropriate rotational speed or torque for the rider in different conditions.
Planetary gear sets are commonly used in the transmission of an electric vehicle. A planetary internal transmission uses a planetary gear train as the principal part of a speed change mechanism which is typically installed in a gear housing of a rear wheel of the vehicle. A planetary internal transmission achieves different rotational speed ratios by changing the gear ratio of the planetary gear train through different input parts, output parts and fixed parts.
The use of a planetary gear train as the principal part of a speed change mechanism in an internal transmission has the following advantages. First, the volume is small and the structure is precise, and there is little limitation to the narrow installation and usage space of the rear wheel hub. Second, the gearshift process works stably. When used in a vehicle in which the rear wheel is driven by a chain, there is no requirement for the chain to be moved to engage with different chain wheels to change a gear ratio, thus the drawback of chain separation is effectively improved, and the transmission efficiency is increased. Third, the speed change mechanism is protected by the external housing of the wheel hub and is not affected by the external environment, thus the usage lifetime is increased. Fourth, the speed change mechanism is installed inside the wheel hub, and there is not as much noise as an external transmission produces during the gearshift process.
According to the transmission principle of the planetary gear train working as a transmission, the sun gear, planet pinion and ring gear each have a respective gear shaft and these three gears spin around one another. In different gear ratios, one of the three gear shafts is fixed and does not spin, another is a driving shaft, and still another is an output shaft. Different combinations result in different gear ratios needed when reducing, increasing and/or reversing the rotational speed. Six possible combination conditions are shown in Table 1 below.
TABLE 1 Possible configurations of planetary gear set.Combination Condition123456Sun GearFixedOutputFixedDrivingOutputDrivingPlanet pinionDrivingDrivingOutputOutputFixedFixedRing GearOutputFixedDrivingFixedDrivingOutput
Therefore, the present invention has been developed using the planetary gear train as the core for a speed change mechanism for use especially with wheeled or electric vehicles. Additionally, environmental issues have significantly promoted the use of electric bicycles and vehicles in recent years. Most electric bicycles and vehicles in use today are equipped with internal transmissions. Thus, internal transmissions have gradually become the research key point of large scale vehicle manufacturers.
Whilst the invention has particular application for use with electrically propelled vehicles such as electric bicycles, it should be understood that the invention is not limited to this field but can find applications in other fields where there is a requirement for a speed change mechanism.